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991.
The condensation of ferrocenecarboxyhydrazide, ferrocenecarboxaldehyde and acetylferrocene with a number of furan derivatives is reported. The reaction of chalcones containing both the furan and the ferrocene nucleus with Phenylhydrazine and hydrazine proceeds to yield pyrazolines. 相似文献
992.
A thermodynamic approach is developed in this paper to describe the behavior of a subcritical fluid in the neighborhood of vapor-liquid interface and close to a graphite surface. The fluid is modeled as a system of parallel molecular layers. The Helmholtz free energy of the fluid is expressed as the sum of the intrinsic Helmholtz free energies of separate layers and the potential energy of their mutual interactions calculated by the 10-4 potential. This Helmholtz free energy is described by an equation of state (such as the Bender or Peng-Robinson equation), which allows us a convenient means to obtain the intrinsic Helmholtz free energy of each molecular layer as a function of its two-dimensional density. All molecular layers of the bulk fluid are in mechanical equilibrium corresponding to the minimum of the total potential energy. In the case of adsorption the external potential exerted by the graphite layers is added to the free energy. The state of the interface zone between the liquid and the vapor phases or the state of the adsorbed phase is determined by the minimum of the grand potential. In the case of phase equilibrium the approach leads to the distribution of density and pressure over the transition zone. The interrelation between the collision diameter and the potential well depth was determined by the surface tension. It was shown that the distance between neighboring molecular layers substantially changes in the vapor-liquid transition zone and in the adsorbed phase with loading. The approach is considered in this paper for the case of adsorption of argon and nitrogen on carbon black. In both cases an excellent agreement with the experimental data was achieved without additional assumptions and fitting parameters, except for the fluid-solid potential well depth. The approach has far-reaching consequences and can be readily extended to the model of adsorption in slit pores of carbonaceous materials and to the analysis of multicomponent adsorption systems. 相似文献
993.
D. A. Chernova A. Kh. Vorob’ev 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(4):575-578
The rotational mobility of a stable fullerene-based nitroxyl radical (fulleropyrrolineoxyl) in toluene was studied. The rotational correlation time of fulleropyrrolineoxyl was found to be about eight times longer than that of 4-oxy-2,2,6,6-tetramethylpiperidine-1-oxyl. The activation energy of the rotational motion of both probes was determined and their hydrodynamic radii estimated. 相似文献
994.
An automated, continuous-flow system is utilized to determine specific conductance and pH simultaneously in natural waters. A direct electrometric procedure is used to determine values in the range pH 4–9. The specific conductance measurements are made with an electronically modified, commercially available conductivity meter interfaced to a separate module containing the readout control devices and printer. The system is designed to switch ranges automatically to accommodate optimum analysis of widely varying conductances ranging from a few μmhos cm-1 to 15,000 μmho cm-1. Thirty samples per hour can be analyzed. Comparison of manual and automated procedures for 40 samples showed that the average differences were 1.3% for specific conductance and 0.07 units for pH. The relative standard deviation for 25 replicate values for each of five samples was significantly less than 1% for the specific conductance determination; the standard deviation for the pH determination was ? 0.06 pH units. 相似文献
995.
Reversed-phase high-performance liquid chromatography of proteins, traditionally carried out with strong acids like trifluoroacetic acid or phosphoric acid, which can damage reversed-phase columns, can be performed with excellent results using the far milder formic acid in the presence of salt. For certain separations, dynamic coating of the column with crown ethers can bring added resolution. Examples given are for peptides from a digest of methionine growth hormone, protein separations from whey proteins containing alpha-lactalbumin and the beta-lactoglobulins A and B, and bovine and porcine insulins. The separation of methionine-growth hormone from growth hormone is also described. 相似文献
996.
Hydroboration of 1,2-dimethylcyclopentene with BH3·THF affords a product in which boron migrates at low temperature into the cyclopentane ring. At higher temperatures subsequent (non-stereospecific) isomerisation occurs via a competing reaction mechanism. 相似文献
997.
Zusammenfassung Zur Messung geringer226Radium- und222Radongehalte werden auch auf dem Gebiet der Strahlenhygiene verschiedene Verfahren verwendet. Eine zylindrische Szintillationskammer günstigster Abmessungen bietet die Möglichkeit, Personen, die226Ra inkorporiert haben, ohne vorhergehende Anreicherung des Atem-Radons zu kontrollieren sowie Lebensmittel und andere Proben von niedrigem226Ra- und222Rn-Gehalt zu analysieren.
Measurement of small amounts of radium and radon
Summary Various procedures employed for the measurement of slight226radium and222radon contents have also been used for the radiation hygiene. A cylindrical scintillation chamber of the most favorable dimensions offers the possibility of checking persons who have incorporated226Ra, without prior concentration of the breath-radon, and also in the analysis of foods and other samples that contain minute amounts of226Ra and222Ra.相似文献
998.
V. D. Gusev T. K. Mitrofanova O. N. Tolkachev R. P. Evstigneeva 《Chemistry of Natural Compounds》1974,8(1):6-9
Summary 1. The condensation of the anomeric methyl 2,3-di-O-benzyl-D-xylofuranosiduronaldehydes with nitromethane has been studied.2. It has been shown that the position of the substituent at the glycosidic center has an influence on the steric directivity of this reaction.3. The structure of the 6-nitro-6-deoxyhexofuranosides synthesized has been confirmed by their conversion into known derivatives of methyl D-glucofuranosides.Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 8–12, January–February, 1972. 相似文献
999.
Micelles of different amphiphiles adopt different shapes and internal packing arrangements in water, depending on their chemical
structures and the conditions of the medium. Two microenvironmental features, namely the polarity and the microviscosity that
the aggregate offers to a solubilized molecule, have been monitored using extrinsic fluorescence probes. While the differences
between micelles of spherical and rod-like shapes are not always distinct, stacked micelles and peptide micelles offer distinctly
lower polarity and higher microviscosity to solubilizates than the others. 相似文献
1000.
Zusammenfassung In der vorliegenden Arbeit wird das Sedimentations-gleichgewicht des Systems Na6[H2W12O40]-NaClO4-H2O bei 25 °C untersucht. Die scheinbare Ladungszahl des Natriummetawolframats wird als Funktion der NaClO4-MolalitätmNaClO4 ermittelt. Aus dieser Abhängigkeit kann für die summarische Dissoziation des NatriummetawolframatsNa2[H2W12O4o] 6Na+ + [H2W12O40]6– die DissoziationskonstanteK in Gegenwart von NaClO4 als Fremdelektrolyt zuK=0,08 mol6·kg–6 bestimmt werden.Der Kreuzdifferentialquotient
(
PXz
, ist der Trace-Aktivitätskoeffizient des Natriummetawolframats) wird ebenfalls als Funktion der NaClO4-Molalität ermittelt.Die Konzentrationsabhängigkeit des Trace-Aktivitätskoeffizienten zeigt einen Verlauf, wie er unseres Wissens nach noch nicht von anderen Autoren beobachtet wurde.
Mit 5 Abbildungen und 1 Tabelle 相似文献
Summary An ultracentrifugal study of the sedimentation equilibrium of the system Na2[H2W12O40]-NaClO4-H2Oat 25 °C is presented. The dependency of the apparent charge of the sodium metatungstate on NaClO4-molality is investigated. From these data the dissociation constant for the dissociation of the sodium metatungstate in the presence of NaClO4 according to the equationNa[H2W12O40] 6Na+ + [H2W12O40]6– is calculated toK=0.08 mol6·kg–6. The cross differential quotient ( PXz is the trace activity coefficient of the sodium metatungstate) shows a behavior in its dependence on NaClO4-molality which to our knowledge has not yet been reported by other authors.
Mit 5 Abbildungen und 1 Tabelle 相似文献